Olanzapine pamoate depot is the third atypical antipsychotic drug to be available as a long-acting intramuscular injection. It was first disclosed in PCT publication WO00/18408 and is structurally represented as below:

It is developed by Eli Lilly and is approved in USA and Europe for the treatment of schizophrenia. Olanzapine long acting injection (LAI) is a salt of pamoic acid and olanzapine that is suspended in an aqueous solution and is injected into the gluteal muscle. Once injected in the gluteal muscle, the two components of the salt slowly dissociate into separate molecular compounds i.e. olanzapine and pamoic acid.
Rate of dissolution of the salt is slow, allowing for a gradual release of olanzapine into the blood circulation over 2 to 4 weeks.
PCT publication WO2011/091142 assigned to Teva Pharma discloses a process for preparation of olanzapine pamoate monohydrate from olanzpaine, wherein the process comprises refluxing olanzapine with pamoic acid in water for 6 hours, cooling the reaction mixture to 50° C. and stirring at the same temperature for 72 hours.
Further, PCT publication WO0018408 disclose a process for preparation of olanzapine pamoate monohydrate from olanzpaine which comprises mixing olanzapine with pamoic acid in the solvents such as N-Dimethyl sulfoxide, tetrahydrofuran, DMSO, acetone and the reaction time is less than one hour.
The processes for preparation of olanzapine pamoate monohydrate from olanzapine as described in the above prior arts require costly solvents and requires longer reaction time. Therefore, there exists a need to have a simple, cost-effective, efficient and commercially viable process for industrial scale preparation of olanzapine pamoate by employing cost effective solvents and requiring minimum reaction time for commercial production.